Diffuser for centrifugal compressors



Sept. 27, 1932. c. w. SMITH DIFFUSER FOR CENTRIFUGAL COMPRESSORS Filed April 13, 1951 Patented 27, 1932 UNITED STATES PATENT orrlcs crmsrnn w. smrrn, or LYNN, massaonusnrrs, assieNoa 'ro GE ERAL ammo COMPANY, A CORPORATION or NEW YORK DIFFUSER FOR GENTRIFUGAL GOMIPBESSbRS Application filed April 13, 1931. Serial No, 529,697.

The present invention relates to centrifugal compressors having difi'users comprising discharge vanes for converting velocity energy into pressure energy and is especially applicable to centrifugal compressors used as supercharges for internal combustion engines, although it is not limited thereto necessarily.

If a centrifugal compressor to be used as a supercharger is built into an internal combustion engine so as to form a unitary part of the engine, the condition is met that certain parts of the engine, for example, timing shafts, lubrication pipes or the like, pass through the difi'user casing in the region'of the diffuser vanes, making it necessary to design the diifuser with these obstructions in mind, and to build the discharge vanes around the obstructions. This may necessitate an unsymmetrical arrangement of the discharge vanes. In connection with superchargers of this type, difficulty has been experienced inefl'ecting an even feeding of mixture to the engine cylinders, with the result that certain cylinders have had a tendency to run hot at higher loads, said cylinders then becoming the limiting factor in the loading of the engine. v.

The object of my invention is to provide an improved construction and arrangement of discharge vanes in the diffuser of a centrifugal compressor wherein the vanes must be built around an obstruction or obstructions, (a thing which may or may not result in unsymmetrical vanes), whereby there is obtained an even discharge from the diffuser, and in the case of a supercharger an even feeding of mixture to the engine cylin-,

ders, andfor-a consideration of what I believe to be novel and my invention, attention is directed to the following specification and to the claims appended thereto. a

The invention is well adapted for'use in connection with superchargers for radial type internal combustion engines, and in the drawing the figure is a sectional view of a centrifugal compressor embodying the, 'inventlon, intended. for use with'this type of engine. It will be understood, however, that this is only by way of example.

Referring to. the drawing, 1 indicates the casing of a centrifugalv compressor; 2 indicates the shaft on which is mounted the impeller 3, and 4-indicates the diffuser com prising the discharge vanes 5 which define the diffuser passages 6. i

In th drawing, the impeller is viewed from the rear and is partly broken away. The blades of the impeller are indicated at 7, the webs between the blades are indicated at 8, and the entrance buckets are indicated at 9. The impellerillustrated is of the single entrance type, that is, it receives gas on-one side only. As is well understood, such an impeller receives gas at its central portion, the gas being guided to the passages between the blades by the entrance buckets, and discharges the gas radially at its eriphery. The gas discharged from the impe ler passes through the diffuser passages 6 in which velocity energy is converted. into pressure energy. 10 indicates the opening in the casing through'which gas is supplied to the impeller.

In the present instance, the supercharger supplies air to the cylinders of a radial engine and the periphery of the casing is provided with a series of spaced discharge passages 11 connected to the cylinders of the engine, (not shown). Ordinarily, in a supercharger of this type, the impeller is geared to the en gine shaft andthe inlet opening 10 is. connected to the carburetor so that the impeller draws air through the carburetor and discharges, the carbureted mixture of fuel and air to the engine cylinders. 12 indicates shafts which form a part of the engine and which pass through the casing of the super! charger, the shafts being mounted in suitable bearings 13 located in openings in the casing.

According to my invention, I design one of the discharge vanes 5 of a size and shape to permit of the passage through it of the largest shaft or other obstruction encountered,

and I preferably make the other discharge vanes of substantially the same size and shape. The front and rear walls of the discharge vanes are curved togive the desired other obstructions, a thing which may re.-'

sult in an unsymmetrical spacing of the vanes, and in addition I lace the vanes around the periphery of the lmpeller in a manner such that the inlet height a and the discharge height I) of each diffuser passage 6 bear thesame ratio or substantially the same ratio to each other. That is, I so space the discharge' vanes that equals a constant, or'substantially constant. This means that each diffuser passage has substantially the same expansion ratio. This is accomplished in the case of vunsymmetrical vanes by varying the rate of expansion of the diffuser passages, it having been found that the several passages may have varying rates of expansion within limits without affecting adversely the operation of the compressor or its efficiency. The rate of expansion of the diffuser passages may be varied by changing the curvas tu're of the walls of the vanes.

In addition to the foregoing, the discharge vanes are so arranged that the inlet arcs c between discharge vanes bear to the outlet arcs dhthe same, or s'ubstantially the same, ratio, t at is 1 equals a constant, or substantially a constant. a

equals a constant, or substantially a constant.

Furthermore, the outlet passage heights b 7 bear to the corresponding outlet arcs d the same, or substantially the same ratio; that is,

equals a constant, or substantially a 1 constant.

' By the foregoing-arrangement it has been found possible to feed; mixture evenly to a number of cylinders, and as a result to increase the power of-the engine. For example, in the case of a certain engine of 500 horsepower, it was found possible by means of this invention to increase the output of the engine 30 horsepower over the'bes't result's'obtamed with any previous diffuser.

In the present instance, there are four shafts or obstructions 12 passing through the difi'user. These are taken care of by three spaced d scharge vanes. The spacing of these t jree dlscharge vanes is such thatv one additional vane is located the spaces between them in two instances and two additional vanes are utilized in the third instance.

In certain cases it may be found that the application of the above principles will result in diffuser passages of varying efliciency, due to differences in effective length, or varying rates of expansion, or both, which may result in slight'inequality in the amount of mixture discharged at diiferent parts of the periphery. In such cases correction for this condition can be obtained by making the inlet passage heights a slightly disproportionate to the inlet arcs 0, in such a manner that the ratio c, is made slightly greater than the average for passages which are of lower efiiciency, and slightly less than the average for passages which are of higher efliciency. This correction will usually be very small, and in many cases may be neglected.

By a diffuser having unsymmetrical discharge vanes, I mean a diffuser wherein the discharge vanes, which may or may not be alike, are not regularly and evenly spaced.

My invention may be utilized in connection ,with centrifugal compressors in any instance where for any reason it is foundnecessary to build the discharge vanes around 'obstruc tions.

In accordance with the provision of the patent statute, I havedescribed the principle of operation of my invention, together with the'ap'paratus which I now consider to represent the best embodiment thereof; but I desire to have it understood that the apparatus shown is only illustrative and that the invention may be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. A centrifugal compressor comprising a casing, an impeller. and a diffuser having discharge vanes which define diffuser passages, there being an obstruction'or obstructions around which the discharge vanes are built,.

necessitating an uneven spacing of the vanes, characterized by the fact that the vanes although unevenly spaced are so located and arranged that the ratio of the inlet height to the outlet height andof the inlet arc to the outlet arc of the diffuser passages is in each instance substantially a constant.

2. A centrifugal compressor comprising a casing, an impeller, and a diffuser having discharge vanes which define diffuser passages, there being an obstruction or obstructions around which the discharges vanes are built, necessitating an uneven spacing of'the vanes. characterized by the fact that although the diffuser passages are of unequal size the rates of expansion of the diffuser passages are of such valuethat the ratio of the inlet height to the outlet height and of the inlet arc-to the all) hand.

outlet arc of the diffuser passages is in each instance substantially a constant.

3. A centrifugal compressor comprising a casing, an impeller, and a diffuser having unsymmetrical discharge vanes characterized by the fact that the vanes although unevenly spaced are so located and arranged that the ratio of the inlet height to the outlet height and of the inlet arc to the outlet arc of the difi'user passages is in each instance substantially a constant.

4. A centrifugal compressor comprising a casing. an impeller. and a diffuser surrounding the impeller having unevenly spaced curved walls which define diifuser passages for converting velocity energy into pressure energy. said diffuser passages having difierent rates of expansion. the ratio of the inlet hei ht to the outlet height and the inlet are to the outlet are for all the diffuser passages a constant.

5. A centrifugal compressor comprising a casing. an impeller. and a diffuser having discharge vanes which define diffuser passages, therebeing an obstruction or obstrucfirms around which the discharge vanes are built. necessitating an uneven spacing of the vanes, characterized b the fact that the vanes although unevenly spacedare so 10- cated and arranged that the ratio of the inlet height to the inlet arc. the ratio of the outlet height to the outlet arc. and the ratio of, the inlet height to the outlet arc of the diffuser passages is in each instance substantially a constant.

6. A centrifugal compressor comprising a casing, an impeller. and a difiuser having discharge vanes which define diffuser passages. there being an obstruction or obstruc tions around which the discharge vanes are built. necessitating an unequal spacing of the vanes, characterized by the fact that the vanes although unevenly spaced are so locat-- 5 ed and arranged that the ratio of the inlet height to the inlet arc. the ratio of the outlet height to the outlet arc, and the ratio of the inlet arc to the outlet arc of the diffuser passages is in each instance substantially a. constant.

7. A centrifugal compressor comprising a casing. an impeller, and a diffuser having unsymmetrical discharge vanes, characterized by the fact that the vanes although unevenly spaced are so located and arranged that the ratio of the inlet height to the inlet arc and the ratio of the outlet height to the outlet arc is in each instance substantially a constant,

and the ratio of either the inlet height to the outlet height or the inlet arc to the outlet arc is substantially a constant.

In witness whereof, I have hereunto set my CHESTER w. SMITH. 

